Storage medium for data

ABSTRACT

This disclosure relates to a data storage medium, and in particular to a data storage medium comprising at least one high modulus layer. In one embodiment, an asymmetric optical storage medium can comprise: a substrate layer comprising polyarylene ether, a high modulus layer comprising a thermoset, and a data layer disposed between the modulus layer and the substrate layer. The high modulus layer has a tensile modulus that is greater than a substrate layer tensile modulus. In another embodiment, an asymmetric optical storage medium can comprise: a substrate layer comprising polyarylene ether and having surface features and a high modulus layer disposed on the side of the substrate comprising the surface features. The surface features can comprise pits. The high modulus layer can comprise a thermoset, and can have a tensile modulus that is greater than a substrate layer tensile modulus.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/032,417 filed Jan. 10, 2005 now U.S. Pat. No. 7,029,742, which isapplication is a continuation of 10/417,718, filed Apr. 17, 2003, nowU.S. Pat. No. 6,893,700, issued May 17, 2005, which is a continuation ofU.S. application Ser. No. 09/683,500 filed Jan. 9, 2002, now U.S. Pat.No. 6,716,505, which claims priority to U.S. Provisional Ser. No.60/316,534 filed Aug. 31, 2001, all of which are incorporated herein intheir entirety.

BACKGROUND OF INVENTION

This disclosure relates to a data storage medium, and in particular to adata storage medium comprising a high modulus layer used to control theoverall degree of flatness in the storage medium.

An increase in data storage density in optical data storage media isdesired to improve data storage technologies, such as, but not limitedto, read-only media, write-once media, rewritable media, digitalversatile media and magneto-optical (MO) media.

As data storage densities are increased in optical data storage media toaccommodate newer technologies, such as, but not limited to, digitalversatile disks (DVD) and higher density data disks for short and longterm data archives such as digital video recorders (DVR), the designrequirements for the transparent component of the optical data storagedevices have become increasingly stringent. Optical disks withprogressively shorter reading and writing wavelengths have been theobject of intense efforts in the field of optical data storage devices.Materials and methods for optimizing physical properties of data storagedevices are constantly being sought. Design requirements for thematerial used in optical data storage media include, but are not limitedto, disk flatness (e.g., tilt), water strain, low birefringence, hightransparency, heat resistance, ductility, high purity, and mediumhomogeneity (e.g., particulate concentration). Currently employedmaterials are found to be lacking in one or more of thesecharacteristics, and new materials are required in order to achievehigher data storage densities in optical data storage media. Diskflatness, also referred to as tilt, is a critical property needed forhigh data storage density applications. Consequently, a long felt yetunsatisfied need exists for data storage media having improveddimensional stability and minimal tilt.

SUMMARY OF INVENTION

In one embodiment, An asymmetric optical storage medium can comprise: asubstrate layer comprising polyarylene ether, a high modulus layercomprising a thermoset, and a data layer disposed between the highmodulus layer and the substrate layer. The high modulus layer has atensile modulus that is greater than a substrate layer tensile modulus.

In another embodiment, the asymmetric optical storage medium cancomprise: a substrate layer comprising polyarylene ether and havingsurface features, wherein the surface features comprise pits, and a highmodulus layer disposed on the side of the substrate comprising thesurface features, wherein the high modulus layer comprises a thermoset.The high modulus layer has a tensile modulus that is greater than asubstrate layer tensile modulus.

Various features, aspects, and advantages of the present disclosure willbecome apparent with reference to the following detailed description,appended claims, and accompanying figures.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross sectional view of one embodiment of the present datastorage medium (10), wherein the medium comprises a substrate layer(20), which is in direct contact with a data layer (30), the data layer(30), which is in direct contact with a high modulus layer (40), and thehigh modulus layer (40), which is in direct contact with a thin filmlayer (50).

FIG. 2 is a cross sectional view of another embodiment of the presentdata storage medium (60), wherein the medium comprises a substrate layer(70), which in direct contact with a data layer (80), the data layer(80), which is in direct contact with a thin film layer (90), and thethin film layer (90), which is in direct contact with a high moduluslayer (100).

DETAILED DESCRIPTION

The present disclosure describes the use of polymeric material asstorage media for data, wherein this storage medium may have an improveddirectional stability. In one embodiment of the present disclosure, thestorage medium for data (part 10 in FIG. 1; part 60 in FIG. 2) comprisesa plurality of layers comprising at least one substrate layer, at leastone data layer that is in direct contact with the substrate layer, atleast high modulus layer, and at least one thin film layer. As usedherein, the term “high modulus” refers to a tensile modulus typicallygreater than about 1 Gigapascal (Gpa). The high modulus layer can have atensile modulus that is greater than or equal to the substrate tensilemodulus. The high modulus layer effectively increases the dimensionalstability of the data storage medium by reducing the tilt of the datastorage medium. As used herein, the term “tilt” refers to the number ofradial degrees by which a data storage medium bends on a horizontalaxis, and is typically measured as the vertical deviation at the outerradius of the storage medium. Typically, the tilt is half of the averageradial deviation (the deviation of a laser beam) as measured in degrees.

In the context of the present disclosure, a typical data storage mediumis composed of a plurality of polymeric components, which are generallycombined in overlaying horizontal layers of various thicknesses,depending on the specific properties and requirements of the datastorage medium. A major component of a data storage medium is asubstrate layer (part 20 in FIG. 1; part 70 in FIG. 2). The substratelayer is typically made of a polymeric material, which comprises atleast one member selected from the group consisting of a thermoplastic,a thermoset, and any combination thereof. Both addition and condensationpolymers are suitable for the present invention. As used herein the term“thermoplastic polymer”, also referred to in the art as a thermoplasticresin, is defined as a material with a macromolecular structure thatwill repeatedly soften when heated and harden when cooled. Illustrativeclasses of thermoplastic polymers include, but are not limited to,styrene, acrylics, polyethylenes, vinyls, nylons, and fluorocarbons. Asused herein the term “thermoset polymer”, also referred to in the art asa thermoset resin, is defined as a material which solidifies when firstheated under pressure, and which cannot be remelted or remolded withoutdestroying its original characteristics. Illustrative classes ofthermoset polymers included, but are not limited to, epoxides,malamines, phenolics, and ureas.

Illustrative examples of thermoplastic polymers which are suitable forthe substrate layer include, but are not limited to, olefin-derivedpolymers (e.g., polyethylene, polypropylene, and their copolymers),polymethylpentane; diene-derived polymers (e.g., polybutadiene,polyisoprene, and their copolymers), polymers of unsaturated carboxylicacids and their functional derivatives (e.g., acrylic polymers such aspoly(alkyl acrylates), poly(alkyl methacrylates), polyacrylamides,polyacrylonitrile and polyacrylic acid), alkenylaromatic polymers (e.g.,polystyrene, poly-alpha-methylstyrene, polyvinyltoluene, andrubber-modified polystyrenes), polyamides (e.g., nylon-6, nylon-6,6,nylon-1,1, and nylon-1,2), polyesters; polyketones; polycarbonates;polyester carbonates; polyethers such as aromatic polyethers,polyarylene ethers, polyethersulfones, polyetherketones,polyetheretherketones, polyetherimides; polyarylene sulfides,polysulfones, polysulfidesulfones; and liquid crystalline polymers. Inone embodiment, the substrate layer comprises a thermoplastic polyester.Suitable examples of thermoplastic polyesters include, but are notlimited to, poly(ethylene terephthalate), poly(1,4-butyleneterephthalate), poly(1,3-propylene terephthalate),poly(cyclohexanedimethanol terephthalate), poly(cyclohexanedimethanol-co-ethylene terephthalate), poly(ethylenenaphthalate), poly(butylene naphthalate), and polyarylates. For example,the substrate layer can comprise a polyester, a polycarbonate, apolystyrene, a polymethylmethacrylate, a polyketone, a polyamide, anaromatic polyether, a polyether-sulfone, a polyether-imide, a polyetherketone, a polyphenylene ether, a polyphenylene sulfide, and anycombinations thereof.

In another embodiment the substrate layer comprises a thermoplasticelastomeric polyesters (TPEs). As defined herein, a thermoplasticelastomer is a material that can be processed as a thermoplasticmaterial, but which also possesses some of the properties of aconventional thermoset resin. Suitable examples of thermoplasticelastomeric polyesters include, but are not limited to, polyetheresters,poly(alkylene terephthalate), poly(ethylene terephthalate), poly(butylene terephthalate), polyetheresters containing soft-block segmentsof poly (alkylene oxide) particularly segments of poly(ethylene oxide)and poly(butylene oxide), polyesteramides such as those synthesized bythe condensation of an aromatic diisocyanate with dicarboxylic acids,and any polyester with a carboxylic acid terminal group.

Optionally, the substrate layer can further comprise at least onedielectric layer, at least one insulating layer, or any combinationsthereof. The dielectric layer(s), which are often employed as heatcontrollers, typically have a thickness between about 200 Å and about1,000 Å. Suitable dielectric layers include, but are not limited to, anitride layer (e.g., silicone nitride, aluminum nitride), an oxide layer(e.g. aluminum oxide), a carbide layer (e.g., silicon carbide), and anycombinations comprising at least one of the foregoing and any compatiblematerial that is not reactive with the surrounding layers.

In the context of the present disclosure, a typical data storage mediumfurther comprises at least one data layer (part 30 in FIG. 1; part 80 inFIG. 2). The data layer, which typically comprises a reflective metallayer, can be made of any material capable of storing retrievable data,such as an optical layer, a magnetic layer, a magneto-optic layer. Thethickness of a typical data layer can be up to about 600 Angstroms (Å).In one embodiment, the thickness of the data layer is up to about 300 Å.The information which is to be stored on the data storage medium can beimprinted directly onto the surface of the data layer, or stored in aphoto-, thermal-, or magnetically-definable medium which has beendeposited onto the surface of the substrate layer. Suitable data storagelayers are typically composed of at least one material selected from thegroup consisting of, but are not limited to, oxides (e.g., siliconeoxide), rare earth element-transition metal alloys, nickel, cobalt,chromium, tantalum, platinum, terbium, gadolinium, iron, boron, organicdyes (e.g., cyanine or phthalocyanine type dyes), inorganic phase changecompounds (e.g., TeSeSn or InAgSb), and any alloys or combinationscomprising at least one of the foregoing.

The reflective metal layer(s) should be of a thickness that issufficient to reflect an amount of energy, which is sufficient to enabledata retrieval. Typically, a reflective layer has a thickness up toabout 700 Å. In one embodiment the thickness of the reflective layer isin between about 300 Å and about 600 Å. Suitable reflective layersinclude, but are not limited to, aluminum, silver, gold, titanium, andalloys and mixtures comprising at least one of the foregoing. Inaddition to the data storage layer(s), dielectric layer(s), protectivelayer(s), and reflective layer(s), other layers can be employed such aslubrication layer(s), adhesive layer(s) and others. Suitable lubricantlayers include, but are not limited to, fluoro compounds such as fluorooils and greases.

In the context of the present disclosure, a typical data storage mediumfurther comprises at least one high modulus layer (part 40 in FIG. 1;part 100 in FIG. 2). In one embodiment of the present disclosure, asuitable high modulus layer typically comprises a thermoset polymer,which can be cured thermally, cured by ultraviolet (UV) radiation, orcured by any method commonly known to those skilled in the art. Inanother embodiment of the present disclosure, the high modulus layercomprises a thermoplastic polymer. In yet another embodiment of thepresent disclosure, the high modulus layer comprises a combination of athermoset polymer and a thermoplastic polymer. Typically, the highmodulus layer is applied to the storage medium via a spin-coatingprocess, however, any method known to those skilled in the art such as,but not limited to, spray deposition, sputtering, and plasma depositioncan be used to deposit a high modulus layer with a thickness in a rangebetween about 0.01 micrometers (μm) and about 50 micrometers (μm), or,more specifically, about 0.5 micrometers and about 30 micrometers, ontothe data storage medium. Illustrative examples of thermoset polymersinclude, but are not limited to, polymers derived from acrylates,silicones, polyphenylene ethers, epoxies, cyanate esters, unsaturatedpolyesters, multifunctional allylic materials, diallylphthalate,acrylics, alkyds, phenol-formaldehyde, novolacs, resoles, bismaleimides,melamine-formaldehyde, urea-formaldehyde, benzocyclobutanes,hydroxymethylfurans, isocyanates, and any combinations thereof. Somepossible examples of materials for the high modulus layer include: asilicone hardcoat, silica with hydrolizable silanes, a siloxane, anepoxy, a urethane, an imide, and any combination thereof. Other examplesinclude a poly-methylmethacrylate, a methyl methacrylate-polyimidecopolymer, a methyl methacrylate-silicone copolymer, and combinationscomprising at least one of the foregoing. In yet another example, thehigh modulus material can comprise: an acrylate, an epoxy, asilicone-acrylate, a urethane, and any combination thereof. In oneembodiment, the thermoset polymer further comprises at least onethermoplastic polymer, such as, but not limited to, polyphenylene ether,polyphenylene sulfide, polysulfone, polyetherimide, or polyester.Typically, the high modulus layer is a copolycarbonate ester. Thethermoplastic polymer is typically combined with a thermoset monomermixture before curing of said thermoset. In addition the high moduluslayer may be added during the lamination process of the pressuresensitive adhesive.

The data storage medium may also comprise a thin film layer (part 50 inFIG. 1; part 90 in FIG. 2) comprises at least one member selected fromthe group consisting of a homopolymer, a copolymer, a thermoplastic, athermoset, and any mixtures thereof; and further wherein the thermosetis spin coated.

Currently, the dimensions of the storage medium are specified by theindustry to enable their use in presently available data storage mediumreading and writing devices. The data storage medium typically has aninner diameter in a range between about 15 mm and about 40 mm and anouter diameter in a range between about 65 mm and about 130 mm, asubstrate thickness in a range between about 0.4 mm and about 2.5 mmwith a thickness up to about 1.2 mm typically preferred. Other diametersand thickness may be employed to obtain a stiffer architecture ifnecessary.

The storage medium described herein can be employed in conventionaloptic, magneto-optic, and magnetic systems, as well as in advancedsystems requiring higher quality storage medium, areal density, or anycombinations thereof. During use, the storage medium is disposed inrelation to a read/write device such that energy (for instance,magnetic, light, electric, or any combination thereof) is in contactwith the data layer, in the form of an energy field incident on the datastorage medium. The energy field contacts the data layer(s) disposed onthe storage medium. The energy field causes a physical or chemicalchange in the storage medium so as to record the incidence of the energyat that point on a data layer. For example, an incident magnetic fieldmight change the orientation of magnetic domains within a data layer oran incident light beam could cause a phase transformation where thelight heats the point of contact on a data layer.

Numerous methods may be employed to produce the storage mediumincluding, but not limited to, injection molding, foaming processes,sputtering, plasma vapor deposition, vacuum deposition,electrodeposition, spin coating, spray coating, meniscus coating, datastamping, embossing, surface polishing, fixturing, laminating, rotarymolding, two shot molding, coinjection, over-molding of film,microcellular molding, and combinations thereof. In one embodiment, thetechnique employed enables in situ production of the substrate havingthe desired surface features, for example, pits and grooves. One suchprocess comprises an injection molding-compression technique where amold is filled with a molten polymer as defined herein. The mold maycontain a preform or insert. The polymer system is cooled and, whilestill in at least partially molten state, compressed to imprint thedesired surface features, for example, pits and grooves, arranged inspiral concentric or other orientation, onto the desired portions of thesubstrate, i.e., one or both sides in the desired areas. The substrateis then cooled to room temperature.

The following examples are included to provide additional guidance tothose skilled in the art in practicing the claimed invention. Theexamples provided are merely representative of the present disclosure.Accordingly, the following examples are not intended to limit theinvention, as defined in the appended claims, in any manner.

EXAMPLES

Circular data storage disks were prepared as follows. A substrate layerof 4,4-isopropylidenediphenol-polycarbonate polymer (BPA-PC) was moldedinto circular disks about 1.1 mm thick, and with an inner radius ofabout 15 mm and an outer radius of about 120 mm. A metallic data layer,of about 500 Angstroms thick, was sputtered to one of the surfaces ofthe BPA-PC substrate disks. Various thicknesses, described in table 1,of an acrylic lacquer layer (Daicure SD-698) were spin coated onto themetallic data layer of the disks, and the lacquer was cured using UVradiation. A co-polycarbonate-ester thin film of about 75 micronthickness, was bonded to the acrylic layer of the disks using a 25micron thickness pressure sensitive adhesive of negligible modulus, toyield circular data storage disks with a layer configuration similar tothat disclosed in FIG. 2. The data storage disks were equilibrated in anenvironment of a humidity of about 50%. The data storage disks were thentransferred from this first environment of an initial humidity of about50%, to a second environment with humidity of about 90%. The tilt of thedata storage disks was measured over time at a radius of 55 mm while thedisk equilibrated in the 90% humidity. The results of the maximum radialtilt measured over the dynamic as the disks re-equilibrated to the 90%humidity environment for the data storage disks with varying thicknessof the spin-coated high modulus layer are described in Table 1.

TABLE 1 High Modulus Lacquer Maximum Radical tilt thickness (microns) at55 mm (degrees) 0 0.316 6.6 0.196 14.6 0.127 27.1 −0.171

As disclosed by the results in Table 1, the addition of the high moduluslacquer layer to the data storage disks reduces the radial tilt-of thedisks during the dynamic period during which the data storage disks areequilibrating from the first to the second humidity level.

While the invention has been illustrated and described, it is notintended to be limited to the details shown, since various modificationsand substitutions can be made without departing in any way from thespirit of the present disclosure. As such, further modifications andequivalents of the invention herein disclosed can occur to personsskilled in the art using no more than routine experimentation, and allsuch modifications and equivalents are believed to be within the spiritand scope of the disclosure as defined by the following claims.

1. An asymmetric optical storage medium, comprising: a substrate layercomprising polyarylene ether; a high modulus layer comprising athermoset, wherein the high modulus layer has a tensile modulus that isgreater than a substrate layer tensile modulus; and a data layerdisposed between the high modulus layer and the substrate layer.
 2. Theoptical storage medium of claim 1, wherein the thermoset comprises anultra-violet light cured thermoset.
 3. The optical storage medium ofclaim 1, wherein the thermo set was derived from a material selectedfrom the group consisting of an acrylate, an epoxy, and a silicone. 4.The optical storage medium of claim 3, wherein the thermoset was derivedfrom a silicone-acrylate.
 5. The optical storage medium of claim 1,wherein the thermoset comprises silica with hydrolizable silanes.
 6. Theoptical storage medium of claim 1, wherein the thermoset comprises asilicone hardcoat.
 7. The optical storage medium of claim 1, wherein thedata layer comprises imprinted data.
 8. The optical storage medium ofclaim 1, wherein the substrate layer comprises surface features, whereinthe surface features comprise pits, and wherein the data layer is areflective layer.
 9. The optical storage medium of claim 1, comprisinganother data layer.
 10. The optical storage medium of claim 1, whereinthe substrate layer comprises surface features, and wherein the surfacefeatures comprise grooves.
 11. The optical storage medium of claim 1,wherein the data layer comprises an inorganic phase change compound. 12.The optical storage medium of claim 1, wherein the data layer comprisesan organic dye.
 13. The optical storage medium of claim 1, wherein thedata layer comprises a reflective material is selected from the groupcomprising silver, silver alloys, and combinations comprising at leastone of the foregoing.
 14. The optical storage medium of claim 1, thesubstrate further comprises a dielectric layer and wherein thedielectric layer comprises aluminum nitride.
 15. The optical storagemedium of claim 1, further comprising: a reflective layer disposedbetween the high modulus layer and the substrate layer; an initialdielectric layer disposed between the data layer and the substrate; andan additional dielectric layer disposed between the data layer and thehigh modulus layer.
 16. The optical storage medium of claim 1, whereinthe substrate layer further comprises polystyrene.
 17. An asymmetricoptical storage medium comprising: a substrate layer comprisingpolyarylene ether and having surface features, wherein the surfacefeatures comprise pits; and a high modulus layer disposed on the side ofthe substrate comprising the surface features, wherein the high moduluslayer comprises a thermoset, and wherein the high modulus layer has atensile modulus that is greater than a substrate layer tensile modulus.18. The optical storage medium of claim 17, further comprising areflective layer disposed between the high modulus layer and thesubstrate layer.
 19. The optical storage medium of claim 17, wherein thesubstrate layer further comprises polystyrene.
 20. An asymmetric opticalstorage medium comprising: a substrate layer comprising polyaryleneether and having surface features, wherein the surface features comprisegrooves; and a high modulus layer disposed on the side of the substratecomprising the surface features, wherein the high modulus layercomprises a thermoset, and wherein the high modulus layer has a tensilemodulus that is greater than a substrate layer tensile modulus.